In recent years, supercritical fluid processing devices such as supercritical fluid supercritical fluid chromatography (hereinafter SFC: Supercritical Fluid Chromatography) and a supercritical fluid extraction device (hereinafter SFE: Supercritical Fluid Extraction) that perform analysis and extraction of a sample by using a supercritical fluid are gaining attention. A supercritical fluid has the properties of both a liquid and a gas, and is characteristic in that it has higher diffusivity and lower viscosity than a liquid, and by using the supercritical fluid as a solvent, fast, high-resolution, high-sensitivity analysis, or highly accurate extraction is enabled.
The SFC is chromatography that is performed by applying constant temperature and pressure to carbon dioxide or the like to obtain a supercritical fluid, and by using the supercritical fluid as a solvent. Generally, to keep the solvent in a supercritical state, the flow rate has to be a micro flow rate of 3 ml/min or less, and the pressure of the flow path system has to be 10 MPa or more. Accordingly, an SFC device is provided with a pressure control valve, at a post-stage side of an analytical column, for maintaining the flow path system at a constant pressure of 10 MPa or more. The same thing can be said for the SFE.
As the pressure control valve, those that adopt a method of adjusting a gap (an opening area) between a valve seat provided with an inlet flow path and a valve member clogging the inlet flow path (see Patent Document 1), a method of adjusting the flow path width (an opening area) by driving of a diaphragm (see Patent Document 2), a method of inserting a needle into an orifice opening at an end of an inlet flow path and adjusting the gap (an opening area) based on the insertion depth of the needle into the orifice opening (see Patent Document 3), and the like may be cited.